Subject: [mobile-ip] Mobile Prefix Advertisements

From: [email-masked]
Date: Wed, 25 Sep 2002 14:26:33 +0530

Hi,

With reference to draft-18, I have some doubts regarding Mobile Prefix
Advertisements

Section 10.9.2 : Scheduling Prefix Deliveries to the Mobile Node
   "The home agent uses the following algorithm to determine when to send
   prefix information to the mobile node.

    -  If the mobile node has not received the prefix information within
       the last HomeRtrAdvInterval seconds, then transmit the prefix
       information.  This MAY be done according to a periodically
       scheduled transmission."

1) What is "HomeRtrAdvInterval" and how it is communicated to MN?Is it a
contant value?

Section 11.3.3: Sending Mobile Prefix Solicitations
   "The mobile node SHOULD send a Solicitation to the home agent when
   its home address will become invalid within MaxRtrAdvInterval
   seconds, where this value is acquired in a previous Mobile Prefix
   Advertisement from the home agent.  If no such value is known, the
      value MAX_PFX_ADV_DELAY seconds is used instead (see section 12)."

2) How "MaxRtrAdvInterval" is conveyed to MN? Is it through
"AdvIntervalOption"?
3) What should be the value of "MaxRtrAdvInterval"?

For Mobile IPv6 the MaxRtrAdvInterval is 1.5 secs.

4) How MaxRtrAdvInterval is similar to MAX_PFX_ADV_DELAY ?

In my opinion "MaxRtrAdvInterval" should be "HomeRtrAdvInterval". Please
correct me if i am wrong.

thanks
Sourajeet...

---

From: "T.J. Kniveton" <[email-masked]>
Date: Wed, 25 Sep 2002 10:13:02 -0700

> With reference to draft-18, I have some doubts regarding Mobile Prefix

Sorry that it is not fully clear. I will try and answer your questions below.

> 1) What is "HomeRtrAdvInterval" and how it is communicated to MN?Is it a

It is the Home Router Advertisement Interval. I.e., the interval at which
Router Advertisements are sent on the home network. Yes, it is a constant value
based on the configuration of the home agent.

> 2) How "MaxRtrAdvInterval" is conveyed to MN? Is it through

Yes, it could be conveyed through that option.

> 3) What should be the value of "MaxRtrAdvInterval"?

In section 7.5, MaxRtrAdvInterval is defined.

> For Mobile IPv6 the MaxRtrAdvInterval is 1.5 secs.

Yes, this is true, and this is a problem. The MPAs should be sent periodically,
but not nearly that often. I will address this in another, follow-up e-mail.

> 4) How MaxRtrAdvInterval is similar to MAX_PFX_ADV_DELAY ?

Here is my personal interpretation:

MaxRtrAdvInterval is the maximum amount of time that the Home Agent should wait
in between sending Router Advertisements on the home link. MAX_PFX_ADV_DELAY is
the maximum amount of time it is estimated that prefix advertisements will be
delayed in transit. MaxRtrAdvInterval is more related to the characteristics of
the network, as in how often prefixes might change, how likely it is for a node
to spontaneously turn on or lose its prefix information, etc.
MAX_PFX_ADV_DELAY, on the other hand, is solely related to the latency,
distances between nodes, and number of gateways in the network.

This is unrelated to the question you asked above, about what MPAs should use,
which I will write another e-mail about as promised.

> correct me if i am wrong.

No, the HomeRtrAdvInterval is the amount of time between RAs. The
MaxRtrAdvInterval is the maximum value for HomeRtrAdvInterval.

> Sourajeet...

-TJ

-- 
        T.J. Kniveton 
   Communication Systems Lab
     Nokia Research Center